PREFACE TO THE THIRD EDITION. 



The general plan and scope of this outline of histology are the 

 result of experience in teaching this subject to students of medicine 

 under conditions which require economy of time. In order to 

 accomplish the greatest amount of instruction under these circum- 

 stances it seemed necessary to present, early in the course, certain 

 generalizations which might be kept constantly in mind and assist 

 the memory in retaining facts by showing their logical correlation. 

 The broad ideas of almost universal applicability which were 

 chosen for this purpose were : first, the conception of the cell as the 

 active constituent of tissues ; second, the general rule that the ele- 

 mentary tissues are composed of cells and intercellular substances, 

 and that their differences depend upon the proportions or characters 

 of those constituents ; third, that the structural details of the dif- 

 ferent tissues are intimately correlated to their usefulness — i. e., 

 that function and structure are mutually dependent upon each 

 other, being but two aspects of a single device or arrangement ; 

 and, fourth, that the ability of tissues to perform active functions 

 is, in the main, roughly proportional to the number or size of the 

 cells entering into their structure. 



The author believes that his experience has shown that the early 

 introduction of these fundamental ideas has been a distinct aid to 

 the student ; and it is his belief that such would also be the case no 

 matter to what limits the course of instruction in this subject might 

 be extended. 



In the elaboration of these ideas the author has been in the habit 

 of arbitrarily dividing the activities of the cells of the body into 

 four theoretical groups : the reproductive activities, leading to the 

 production of new cells; the formative activities, through which the 

 structural modifications resulting in the formation of different varie- 

 ties of tissue were brought about ; the nutritive activities, maintain- 

 ing the integrity of the tissues already formed ; and the functional 



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